Figure 4.

Activated platelet-induced CD16 expression on monocytes is involved in CD16-dependent phagocytosis. Purified CD14⁺CD16^- monocytes were co-cultured with resting platelets or APD-activated platelets for 18 h Monocytes were incubated for 15 min with latex beads coated with FITC-labeled rabbit IgG. The phagocytic activity of monocytes was analyzed using flow cytometry. (A) Representative histogram plots of latex bead-based phagocytic activity of monocytes. To evaluate CD16-dependent phagocytic activity, CD64 and CD32, both Fcγ receptors, were blocked for 30 min by anti-CD64 and anti-CD32 neutralizing antibodies (10 μg/ml of each antibody) and their phagocytic activity was quantified in monocytes co-cultured with resting platelets or ADP-activated platelets and with or without anti-CD16 neutralizing antibody (10 μg/ml). (B) Frequency (%) of monocyte phagocytosis of latex beads coated with FITC-labeled rabbit IgG under the indicated conditions. (n = 6) (C) Correlation between CD16-dependent phagocytic activity and the frequency of CD14⁺CD16⁺ monocytes after 18 h-co-culture with ADP-activated platelets (n = 7). P value was obtained using the Pearson correlation analysis. Bars show the mean ± S.E.M. *p < 0.05 and **p < 0.01 by two-tailed paired t-test.